Tuesday, 13 March 2018

Twenty years later: Offline vs Realtime Rendering

Just like its predecessor Riven was a game composed of prerendered CGI images. Twenty years later Obduction a sequel in series was created as realtime with the unreal engine. Given the advancement of hardware and CGI algorithms over 20 years how do these two compare?

Comparison validity

It does not initially seem fair to compare offline rendering to realtime (desktop) rendering. Beyond simply stating that this analysis will be qualitative the following arguments can be made:

Performance

Riven was rendered offlline using 13 SGI Indigo workstations. The performance estimate for this as though it is a single server is likely no more than ~2.0 Gflops. In contrast today something like a gtx 1070 has on the order of 6 Tflops. Worst case frame time for an offline render in riven was an hour or less. While Obduction is fully realtime (30 fps) it uses temporal super sampling that can require up to half a second to settle. Resolution in Riven is at least 1/4 the pixel density of realtime however it is extremely difficult to draw a quantitative comparison due to scene complexity. The original offline rendering still likely has 2-6 times the raw compute power available to it per frame over the realtime advancements.

Tools and Budget

There are likely no first order arguments that exist that would suggest that CGI workflow tools have degraded in performance and usability. It should be much easier to create high quality 3d scenes in 2013 than in 1993. Riven had a budget of ~4 million (2013 dollars) with a development time of 4 years. This contrast with the smaller budget of 2.5 million (2013 dollars) and 3 year dev time for Obduction.

Style

Finally to do qualitative comparisons of images we should first make it clear that this is an apples to apples comparison. The graphical style of Riven and Obduction are the same in the following ways.

Conclusion

Graphically Riven is a significantly better work. It stands to reason that it should be possible to achieve the graphical quality of riven in realtime today. Advancements in computer performance, content tools, and graphic algorithms lend credence to this idea. Obduction however is not a data point in support of this theory.[update]
There apparently is a realtime version of riven in development called Starry Expanse. We will have to see what the end product looks like but the results already appear to be an improvement over Obduction. (See images at http://www.starryexpanse.com/2017/06/10/stacking-shelves-gehns-lab/)